This invention relates to a synthetic resin bottle, and in particular, to a synthetic resin bottle that resists deformation caused by pressure force coming from a lateral direction.
Synthetic resin bottles made of a polyethylene terephthalate resin (hereinafter referred to as a PET resin) and the like have been in wide use until today as the containers for various drinks. With a trend toward thin body wall intended for material cost reduction, the bottle shape design has to face large problems, including how to secure full strength and rigidity as the bottle and how to obscure the body wall deformation caused by pressure fluctuation inside the bottle.
For example, Japanese Published patent application JP-A-1998-58527 includes descriptions concerning a bottle having vacuum-absorbing panels in the body portion. This bottle is used for the so-called hot filling process in which the bottle is filled with such contents as juice, tea, etc., which require sterilization at about 90 degrees C. Since the bottle is filled with the contents at about 90 degrees C., then capped, sealed, and cooled, the bottle inside is put under a fairly reduced pressure condition, and the bottle wall deformation becomes problematic.
FIG. 5 shows a small, round PET bottle of a conventional type, having a capacity of 280 ml. The bottle comprises a neck 102, a shoulder 103, a body 104, and a bottom 105. The body 104 is provided with six vacuum-absorbing panels 111 which are dented from body wall. These vacuum-absorbing panels 111 have broadly flat surfaces, but if the inside of the bottle 101 is put under a reduced pressure condition, the panels can be further dented inward easily. In its appearance, the bottle gives no impression of distorted deformation. That is, the vacuum-absorbing panels 111 are capable of inconspicuously performing a function of absorbing the reduced pressure or alleviating the reduced pressure condition (hereinafter referred to as the vacuum-absorbing function).
In the meantime, rigidity or buckling strength (hereinafter referred to simply as the strength) against the pressure force acting in the direction of central axis X of the bottle (hereinafter also referred to as the vertical direction) is predominantly borne by pillar sections 115 formed upright between adjacent vacuum-absorbing panels 111. The rigidity or buckling strength against the pressure force acting in the direction perpendicular to the central axis X (hereinafter referred to as the lateral direction) (See the direction of outline arrows in FIG. 5) is borne by short cylindrical circular sections 116t, 116b, which are disposed in the portions on and under the vacuum-absorbing panels 111. If necessary, each of these circular sections are provided with a circumferential groove 117 which largely performs a function of a circumferential rib to increase the rigidity and the buckling strength in the lateral direction. Owing to the pillar sections 115 and the circular sections 116t and 116b, the rigidity and strength in both of vertical and lateral directions can be secured for the bottle, with no trouble of deformation, in the production, distribution, and sales, including the process of filling the bottle with the contents, the bottle carrier line, the storage under a stacked condition, the sales by means of vending machines, and the cases where bottles are somehow exposed to external force.
If the body is more and more thin-walled in the future, the body wall will deform when it is exposed to a slight change in inner pressure caused by a change in ambient temperature. This occurs not only in those bottles for use in a hot filling process, such as described above, but also in ordinary bottles for use in normal-temperature filling, such as, for example, aseptic filling wherein the contents are filtered by a ultrafiltration technique to remove bacteria or wherein the contents are flash-pasteurized at a high temperature for a short period and are then filled by aseptic filling at normal temperature. Therefore, a design approach to the shape of bottles for use in hot filling described above can be effectively applied not only to the bottles for use in hot filling, but also to ordinary bottles for use in normal temperature filling. In other words, based on this design approach, it is possible to intentionally form easily deformable vacuum-absorbing panels in a dented state in the body wall to let the panels deal with pressure fluctuation inside the bottle and to secure the bottle rigidity and strength by means of the pillar sections and the circular sections that are left undented and disposed to surround the vacuum-absorbing panels.
However, small bottles with a capacity of 350 ml or 280 ml have a problem in that they are limited in the area where vacuum-absorbing panels can be formed, as compared to larger bottles, thus making it difficult to secure satisfactorily both of the vacuum-absorbing function of the vacuum-absorbing panels and the rigidity of the bottle. The bottle rigidity in the vertical direction can be secured relatively easily by the upright pillar sections 115 shown in FIG. 5, but the rigidity and strength in the lateral direction are difficult to secure. If lateral rigidity and strength were not enough, the bottles would not be carried smoothly by the carrier line because their alignment on the line is disturbed. Bottles would also deform when they are packed horizontally in boxes and are stacked for storage. Inside the vending machines, many bottles are stacked horizontally. Under this condition, the body of a lowermost bottle would come in contact with the stopper for discharge and would be distorted in the lateral direction. As a result, the bottle would come free from the stopper, and a crucial problem arises in that a few bottles would be discharged at a burst.
The rigidity and strength of the bottle in the lateral direction can be increased by additionally disposing a circumferential ridge or groove at a position of middle height of the body to let the ridge or groove serve as a circumferential rib. However, such a circumferential ridge or groove would limit the area in which vacuum-absorbing panels can be formed, and it would not be possible to fully secure the vacuum-absorbing function. The smaller the bottle size, the harder it would be to solve this problem, as described above. Fact is that these rigidity and strength have been secured so far by thickening the bottle wall. As a result, there has been an increase in the volume of resin to be used, which resulted in a higher production cost.